Most automobile and truck windshields are comprised of a multi-layer laminated safety glass. Such a windshield is typically comprised of inner and outer layers of glass, each laminated to a plastic intermediate layer, commonly composed of a polybutyrate material. When this type of windshield is struck by a piece of flying debris, for example, a small stone or piece of gravel, a shatter crack is likely to occur. Variously in the prior art, such shatter cracks are referred to as "stars", "bullseyes", etc. In the majority of these cases, the integrity of only the outer layer of glass is breached, and the dissipation of the shattering force distributes outward from the point of impact as it moves inwardly toward the glass, resulting in a roughly conical shatter cone directly beneath the point of impact, said cone being separated from the rest of the outer glass pane by a small cavity. The base of the shatter cone itself is usually still firmly affixed to the intermediate plastic layer. As the cavity is usually open at the point of impact to the environment, it is vulnerable to the penetration of water and other materials. If this occurs, the stresses encountered in the glass due to the thermal expansion of the water caused by sunlight and other environmental factors, can result in delamination of the outer glass pane from the intermediate plastic layer, propagation of the crack, or other damages. These damages are particularly bothersome when the shatter crack is located in or near the line of sight of the driver of the vehicle, as they obstruct or distort his or her vision. If the impact damage is not repaired and the crack propagates, many State auto inspection laws will require that the windshield be replaced. This is certainly a costly and undesirable result.
Many U.S. patents teach a method of repairing a shatter crack in a multi-layer laminated safety glass. The preferred method of repair is to fill the cavity area with a liquid polymer resin and to cure the resin in place by the application of heat, ultraviolet radiation, or other curing stimulus, so that the cavity will be sealed with a solid material that blocks further water intrusion or penetration. Further, the polymer simulates the index of refraction of the glass, resulting in a disappearance of the shatter crack. The prior art extensively teaches the need to inject the liquid polymer resin under vacuum conditions to achieve good penetration of the liquid polymer into the cavity.
The inventor of the present invention, however, knows that it is more important to remove trace amounts of water than it is to achieve a good vacuum in effecting a proper repair. If trace amounts of water are sealed into place by the injected polymer, the water, being a virtually incompressible fluid that is subject to large thermal expansion, will cause the crack to propagate, in spite of the repair. Also, it is well known that water may deleteriously affect the proper bonding or setting of certain liquid polymer resins.
At least one patent in the prior art does teach the need for removal of moisture from the cavity. U.S. Pat. No. 3,765,975, to Hollingsworth, teaches a method of cleaning the impact area with a cloth slightly moistened with toluene, methylethyl ketone, or other suitable volatile solvents, and heating under a vacuum. Hollingsworth, in fact, shows a desired temperature and pressure range in FIG. 2 of his patent for effecting a repair. However, Hollingsworth states that a good method of drying off the cavity is to apply "gentle heat" from the reverse surface of the glass. The economics of doing windshield repairs, the present inventor regrets, do not permit the timely techniques taught by Hollinsworth.
Also, the inventor has learned from his experience that it is critically important to use a heat source that is substantially similar in size to the crack to be repaired. Since the impact of the piece of debris that has caused the shatter crack often leaves unrelieved stresses in the glass, a general application of heat to the glass can result in delamination of the glass or propagation of the crack and render the crack unrepairable. One method found to be extremely undesirable as a heat source is the convective heat provided by a conventional portable hair dryer or an open flame, as from a butane torch.
A first object of the present invention is to provide a portable directed source of radiative heat capable of being placed proximate to a plate of laminated safety glass having a shatter crack, to evaporate the water or other liquid contained in the crack for repairing the crack.
A second object of the invention is to provide such a device than can be powered by an electrical supply already available in a vehicle such as an automobile.
A further object is to provide a method for removing water or other liquid contained in the cavity of such a shatter crack.
These and further objects of the present invention are achieved by a device comprising a means for electrically generating radiative heat which is contained in a housing, the housing being affixed to a handle means. The radiative heat means is sized to approximate the diameter of the shatter crack on which the device is intended to be used. The housing comprises a material that conductively dissipates heat. The device further comprises a means for communicating a source of electrical energy communicated to the radiative heat means, with a means for controlling the flow of the electrical energy disposed along the handle means.
Other objects are achieved by a method for removing water or other liquid contained in the cavity of a shatter crack in a plate of multi-layer laminated safety glass, the method comprising: placing a device as described above proximate to the cavity of the safety glass on the same side of the glass as the cavity and energizing the device for a period sufficient to remove the water or other liquid.